This invention relates to poisons and, more particularly, to a poison in the form of a delayed-action insecticide, as opposed to an insecticide in the form of a contact poison, to eradicate an infestation of insects. Specifically, one embodiment of the invention is directed to an effective delayed-action insecticide to destroy the imported fire ant (IFA).
The IFA menace is a real and serious problem. Since accidental introduction of the black imported fire ant at the port of Mobile, Ala. in 1918, and its cousin the red imported fire ant in 1940, also at the port of Mobile, Ala., the IFA has spread rapidly. Its domain now ranges from Mexico to the Atlantic Coast states of the United States.
Imported fire ants damage young plants by gnawing holes in roots, tubers, stalks, and buds. They can attack young, unprotected animals, such as newborn calves and pigs and newly hatched poultry, as well as field workers in rural areas. They infest homes and businesses in urban areas as well. Their stings are painful and pose a threat to health. Venom of the IFA is unlike that of other stinging insects. Some persons are hypersensitive to this venom and can suffer chest pains or nausea and even lapse into a coma from one sting. Mounds damage machinery, hinder mowing operations, and reduce land value in heavily infested regions.
Previously, various materials have been utilized to fight the IFA, such as used oil, gasoline, detergents (laundry products), and large amounts of pesticides. Typically, these materials pollute and harm the environment.
Currently, there is a number of commercial products in the form of pesticides, which are utilized against the IFA. See Philip J. Hamman, "Fire Ants and Their Control," Texas Agricultural Extension Service Publication L-2034, The Texas A&M University System, College Station, Tex., which includes a partial list of products registered as IFA pesticides. These pesticides are typically contact poisons and are effective in killing a wide variety of insects.
Another class of materials occasionally utilized comprises solvents, such as methylene chloride. These solvents are also contact poisons.
All of the above materials have drawbacks. They kill only on contact, and therefore do not kill the queen which is far underground. The result is that one or more new mounds develop a short distance away from the treated site.
Another commercial product, which is specifically targeted at the IFA, is AMDRO (registered trademark of American Cyanamid Company). This product is a delayed-action pesticide advertised to be very effective against the IFA, because it is eventually ingested by the queen. When the queen is killed, the colony vanishes as the current generation ages and dies. Therefore, unlike the earlier mentioned materials, AMDRO can destroy the mound. However, while AMDRO can destroy the mound, it too has a number of drawbacks.
AMDRO loses efficacy following contact with rain or humidity. This is a serious shortcoming, since the IFA domain is primarily along the southern coast of the United States where rainfall is plentiful. Furthermore, the active ingredient in AMDRO is readily degradable, and therefore its shelf life after its container is opened is very short. The manufacturer recommends that the supply of AMDRO be exhausted within a three-day period after opening the bag. Not surprisingly, its effectiveness in the field is also very short. Finally, AMDRO is expensive, and like other expensive pesticides, it cannot be broadcast over large areas economically. The expense of AMDRO also discourages repeat applications. Accordingly, the contact poisons mentioned above, although not as effective as AMDRO under ideal conditions, are more generally utilized.
Another class of materials investigated as potential IFA toxicants is mentioned in R.K. Vander Meer, C.S. Lofgren, and D.W. Williams, "Fluoroaliphatic Sulfones: A New Class of Delayed-action Insecticides for Control of Solenopsis invicta (Hymenoptera: Formicidae)," Journal of Economic Entomology, Vol. 78, No. 6, December, 1985, pp. 1190-1197. Importantly, this article states in the left hand column on page 1196:
"Large-scale RIFA [red imported fire ant] control is most effectively done with toxicants formulated in baits. Formulations consist of the toxicant dissolved in soybean oil and then absorbed onto a suitable carrier (i.e., corn grits, pregel defatted corn grits). Solid suspensions are not suitable because the RIFA workers have a sophisticated and efficient mechanism for filtering submicron particles from ingested food [Citation omitted.] Consequently, oil solubility is an essential property for any potential RIFA toxicant."
Although the article primarily describes fluoroaliphatic sulfones as IFA toxicants, Table 9 of this article, appearing on page 1196, shows test data for various sulfonic acids and sulfonate salts. These materials were formulated at 1.0% concentrations in honey/water (1:1) and tested against the red imported fire ant. Table 9 lists C.sub.8 F.sub.17 SO.sub.3 K, otherwise known as FC-95 available from 3M Company, St. Paul, Minn., which is a sulfonate salt. FC-95 is totally insoluble in vegetable oils, such as soybean oil. Accordingly, this article concludes in the right hand column on page 1196 that "the solubility properties of the compounds listed in Table 9," including FC-95 "make them poor candidates for RIFA control." It is therefore desirable to formulate a delayed-action insecticide based on materials, such as these sulfonic acids and sulfonate salts, which are not soluble in vegetable oil, for use against the IFA, as well as other insects.